The present invention relates to the field of polymers and polymer blends. The invention further relates to muconic acid-containing polyolefins that may be used as compatibilizing agents.
Thermoplastic polymers individually possess properties, such as heat and chemical resistance, impact resistance, stiffness, strength, and the like, that vary greatly from one polymer to another. For some applications a single polymer may be quite satisfactory. However, in certain situations it is desirable to have a plastic that has a combination of properties not found in any single polymer; in such cases, polymer blends are often used to obtain the benefit of the properties of more than one polymer. Unfortunately, polymers typically do not adhere to each other well, so that polymers that one may wish to blend together may not be compatible. For this reason, compatibilizers are used. Useful compatibilizers include copolymers in which one part of the polymer molecule is compatible with one polymer and another part is compatible with a dissimilar polymer. When the compatibilizer is mixed with these dissimilar polymers a compatible blend may be formed. In the case of a reactive compatibilizer, the compatibilizer forms bonds with one or more of the polymers. Block and graft copolymers are often used as compatibilizers. See, e.g., U.S. Pat. Nos. 3,483,273, 3,860,442, 4,081,424, 4,107,130, and 4,110,303, the disclosures of which are herein incorporated by reference.
Polyolefins having functional monomers grafted thereon are known in the art. Acrylic acid grafted polypropylene, for instance, is produced by BP Chemicals, which sells this polymer as part of its POLYBOND.RTM. product line. This product is used as a reactive compatibilizer for preparing polypropylene-polyester and polypropylene-nylon blends. However, acrylic acid grafting causes polyolefins to degrade significantly, reducing the intrinsic viscosity, molecular weight, and other properties of the polymer; furthermore, the active surface area of the product copolymer is relatively low. Graft copolymers of this type are disclosed in U.S. Pat. Nos. 4,455,273 and 4,584,347, the disclosures of which are herein incorporated by reference.
Maleic anhydride grafted polyolefins are also available from BP Chemicals under the POLYBOND.RTM. tradename. However, these polymers are less effective compatibilizers than the acrylic acid graft copolymers for some applications. Furthermore, polyolefin degradation is a significant problem with these graft copolymers, as well.
Muconic acid, also known as 2,4-hexadienedioic acid, has the chemical formula HOOC--CH.dbd.CH--CH.dbd.CH--COOH. Cis,cis-and cis,trans-muconic acid are presently available from Celgene Corporation. Due to its double bonds and diacid functionality, muconic acid can undergo a wide variety of reactions. Many muconic acid derivatives are known, including lactones, sulfones, polyamides, polyesters, thioesters, addition polymers, and other compounds. Such compounds have a wide variety of uses, including use as surfactants, flame retardants, UV light stabilizers, thermoset plastics, thermoplastics and coatings.